Our new (open access) paper uses repeat @HiRISE data to investigate elongating linear dunes on Mars! Linear dunes are weird in general, but these linear dunes form finger-like structures, which grow in the direction of their crests. 1/n https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2020GL088456

You can see in the gif below the tip of a linear dune elongating in a westward direction, just about touching the stoss of a barchan. 2/n

In other examples, we can see barchan dunes in the process of being ejected from the tips of the linear dunes. We probably wouldn't be seeing this if the migration of dunes on Mars wasn't so slow! 3/n

Another weird thing about these linear dunes is that next to the examples shown above, we see other linear dunes which are barely moving at all, which suggests they may be at or near a steady state. 4/n

These particular linear dunes are found in a region of Mars known as Hellespontus Montes and their morphology is particularly striking. 5/n

On Earth (example below from Chad), these type of linear dunes form in sediment limited environments, where the sand is probably coming from a fixed source, such as behind a mesa. The martian linear dunes show a remarkably similar setup. 6/n